Sintered iron bodies and processes therefor



Patented Sept. 9, 1952 SINTERED IRON BODIES AND PROCESSES THEREFORJoseph E. Drapeau,

Jr., Calumet City, Ill., and

James H. Smith and Richard J. Halsted, Hammond, Ind, assignors to TheGlidden Company, Cleveland, Ohio, a corporation of Ohio N Drawing.Application June 17, 1948, Serial No. 33,658

Claims.

This invention relates to improvements in sintered bodies composedpredominantly of copper-coated iron powders, and to processes associatedtherewith.

It is known that thestrength of sintered bodies composed of soft ironpowders can be improved considerably by incorporating copper with theiron powder prior to sintering the body. The copper has beenincorporated in the past either by admixing copper powder with the ironpowder, or by applying a coating of copper to the iron powder by aqueouschemical displacement or electrolytic methods. In a co-pendingapplication of Drapeau et al., Serial No. 33,656, filed June 17, 1948, aprocess is disclosed for applying a coating of copper to ferrous powdersby means of a thermochemical reaction between the ferrous powder andcuprous oxide, cupric oxide or mixtures of these oxides in a protectiveatmosphere. We have now found, howeventhat the atmosphere employedduring the thermal treatment of soft iron powders in effecting thereaction alters the powder in some manner so that the strength ofsintered bodies made from the coated iron powder depends on and varieswith the nature of that atmosphere. We have found especially that byemploying a reducing or inert atmosphere during the thermal coatingoperation, andby subsequently sintering the coated powders in a neutralor reducing atmosphere with or without the concurrent presence of smallamounts of fluxes and/ or metal-containing components, particularlyhigh-strength sintered bodies may be obtained.

It accordingly is an object of this invention to provide a process forproducing high-strength sintered bodies composed predominantly of ironpowders, at least a major part of said iron powders having been coatedwith copper by a thermochemical reaction.

It is a further object to provide a process for producing high-strengthsintered bodies from iron powders which have been thermally coated withcopper, by sintering bodies of the coated powder in hydrogen, nitrogen,carbon monoxide and like neutral or reducing atmospheres, with orwithout the concurrent presence of small amounts of flux and/ormetal-containing components.

These and other objects will be apparent from the following descriptionof the invention.

As disclosed in the Drapeau et al. application identified above, ironpowder may be coated with an adherent film of copper by mixing the ironpowder intimately with finely-divided copper oxide and then heating themixture for ashort time at temperatures between about 1000 F. and

1500 F; in a substantially non-oxidizing, neutral 2 or reducingatmosphere. The amount of copper so deposited on the iron may be variedat will by suitably proportioning the iron powder and finely-dividedcopper oxide, but when the copper coating is applied for the purpose ofproducing a coated molding powder which can be sintered into a strongbody, the amount of copper ranges generally from about 4% to 330% byweight of the iron. During our investigations of thesintering'properties of iron powders coated with such quantities ofcopper, we have found that the iron powders which have been thermallycoated in the manner described in the said 00- pending application ofDrapeau et al., in a hydrogen, carbon monoxide, nitrogenorlike reducingor inert atmospheres produced much; stronger sintered bodies thanotherwise-identical powders coated in an atmosphere such as'c'arbondioxide. The following examples illustrate this effect. f

Examples 1 and-2 Eighty parts of minus 100 Il'lGSh'llOIl powder having ahydrogen loss less than about 1.5% were mixed intimately with .2 part ofstearic acid and 20 parts of minus 7 micron copper oxide powder composedof about 60% cuprous oxide and 40 cupric oxide. The stearic acid wasadded to improve the uniformity with which the oxide coating distributeditself over the surfaces of the iron particles, and to avoid segregationof the mixture. Half of the mixture (designated Batch A) was then heatedin a carbon dioxide atmosphere at 1200 F. for 15 minutes and'afterwardswas cooled in carbon dioxide to room temperature. The other half of themixture (designated Batch B) was heated in a hydrogen atmosphere at 1200F. for '15 minutes and afterwards cooled in hydrogen to roomtemperature. Samples of both batches were then pressed at 40 tons persquare inch into briquettes having the shape of rectangular bars 1%"long by /zf wide by about thick. The bars were then sintered ,,inhydrogen for hour at 2050 Fifand afterthe following results:

ward cooled in hydrogen. Thesinter ed bars were then tested for modulusor ruptura with Modulus of Rupture (lbs. per sq. in.)

Sample 1.-.. sintered bar made from iron powder 45, 000 coated withcopper in carbon dioxide atmosphere (Batch A). 1 Sample 2.... Sinteredbar made from iron powder 70, 000

coated with copper inhydrogen atmos pherc (Batch 13).

3 Similar results were obtained when nitrogen and carbon monoxideatmospheres were tested for comparison-with .a carbon dioxideatmosphere, in that .the nitrogen and carbon :monoxideatsintered inhydrogen at 2050 F. for hour and finally cooled to room temperature inhydrogen. Tests for modulus of rupture iwere rmade in the same mannerasthe tests in Examples 1 and 2.

Coating Operations 7 t v f, V Mtogulus .1 ar. s'o .0 up- Ex. "Iron iFurnace Additives turein Towder Parts of lbs. per Cu Oxide Atmns .Timesq. in.

phere (Hours) '70 T530 3112' 1% ZnO Borax. 97,000

70 30 CO2 d 39,000

90 10 CO1 M 55,000

" 80 "20 "Hz 'M' 75,000

so .20 ,.H2 ..7o,000

80 "20 Atl'lllos 65,000

100 0 None 13, 250

'Machine-proriucedcontrolled atmosphere, containing some free carbonmonoxide and hydrogen, .together with carbOndiOXideandnitmgen.

oniospheres yield higher moduli of -rupture than is "obtained from acarbondioxide atmosphere.

--We havealso found that when hydrogen; nitrogen or carbon monoxideatmospheres, orl mixtures thereof are used in thetherma-L coating op-;eration, the strength of the sintered rbodiesjmade krfroml'theicoated:iron powders may be even; Mr- ';.:.theri improved ,by eincorporating.i-in= the .coated gpowder prior to :sintering small amounts of alkaflineifluxes and for materials containing low-.melting-point whitemetals. Among the alkaline fluxes which wvecontemplate-may be mentionedthe alkali'metal carbonates, nitrates, and borates ('in -glass form)and. lime. Suchfluxeamay be us'ed'inamounts between about -'.*1'%-and-2% by weig'ht of the coated powder. "The metal-containing.components which-may be incorporated I inthe coated powder either bythemselves or in -'-'combination with the alkaline fluxes include zinc,brass; tin, bronze, cadmium, zinc oxide, tin" oxide an'dcadrriium'oxide. Such white-metal-contain- "-'-ing componen'ts'--maybeused in amounts equiva- "ler'irrin-metal content to between about/4-'%--and ---4'% by weigh't of the coated powders. The fol-"-1owing'examples illustrate the-effects'of-such adfditi'ons-offlux-and/on-metal component. In

theseexamplesminus40 mesh iron, powder 'hav- ""ing'=a"hydrogenlossdessthan" about 1.5% was "coated with copper by mixing the iron-powder"with12%"stearicacid (by weight of "the copper .oxide) and the indicated"'percentage'ofmopper "oxide i('by-wei'ght:of the *iron powder) "I-hecop- I per oxide-which was used was .a .IIllXtllIG "composed "of about60% "cuprous oxide and 40% i'f'cupricoxi'de, andwas 'of a fineness'suchthat 123111 particles were .smaller than about -7 microns.

Thecoatimg'of the iron powderswaseffectedv by heating the mixture ofpowdersfor 15minutes -(except where otherwise noted) at 1200 F. in

.-;.either a carbon dioxide, nitrogen or hydrogen atmosphere (asindicated below) and cooling to mom temperature in the same atmosphere.The

"copper-coated powder was vthenmixed .with the indicatedflux and/orindicatedmetal component in the amount indicated, after which themolding mixture was pressed at 40 tons per square inch intoa test barofthe'size'indicated in Examples 1 and 2. The pressed bars were then-.-It"--will beapparentifrom the :foregoingexam- ;plesithat the use of ahydrogen atmosphere in the. :thermal', coating operation is highly:benefiwcialzin gproducing. a'zcopper-coated; powder-which cicani be:Sintered: into a :strong'zsbody, .Wemave :':found, was prefiously;stated; that .otherastrong "reducing 'ratm'ospheres which :are.:;substantially tnon=icarburizingzzor :slightly-rcarburizingi have asimilar 1 effect. .Carbon :monoxide' is .a.substanntiallyr*non#carburizing. atmosphere :under .the ;conditions .:of:time. and :temperature here emzployed as are mixtures of.hydrogenandicarbon 40 m'onoxide in all: proportions. .:&Z\tmospheres'comiiposedtofi carbonmonoxide; hydrogen and nitro- "-:gen, .such .asthose obtained from commercial ..contr'olledaatmosphere ,gas machinesare also frsuita'ble.

i'lhe'. strengthfiof sintered bodies made in ac- ;:cordance with f' theforegoing principles can be rifurth'er improved by repressing andresinter-ing zztheibody. The repressing-and resintering I of bodies madeJfrom 'powders which 'have been coatedwith copperm a carbon-dioxide'atmosphere is particularlybeneficial; since by'this expedientsuch powders can be-manufactured-into sintered bodieswhich are strong-asbodies made J from powders which have been coated ina'jhy- 5:,dmgen,-nitrogen,--or carbon monoxide "atmos phere.

bondioxide atmosphere has on copper-coated iron powders, theseeffectsmaybeoffset'by'pressing-the-powdersat moderate pressures,sintering sot-he body in-the-customaryi atmospheres'then "repressing thesinteredrbody ata higher pressure -and resintering the repressed body.:Forexam- -p1e;-a-niron powderwhi'ch 'had' been coated with -about*18%--of-- copper -in-a carbonnioxide' atmos- 5" phone; whempresse'datj20"tons :per square inch and-sintered 'at' 2050 F; for /2 hour inhydrogen, developed a modulus of .rupture of 2 8;300 p. s. i. Whenacorresponding'sintered1b ar was repressed at 40"-tons, 'p;i s: i. and"Iesinteredat'I2050". F. for f /21101.11, it:develop.ed a modulus of.rupture of "l05j0.00*p."s. i. The strengths .of' sinteredbodies madefrom :iron powders which 'have'been coated with copper in a hydrogenatmosphere L may..'also "be increased appreciably by repressing. and.resinqgteringfallthough such...repressing anderesintering Thuswhateverimpairing effects a car- 7 is seldom needed with such powders,since moduli of rupture of close to 100,000 lbs. or higher may beobtained from the first pressing and sintering thereof, as shown byExample 3.

We have found that copper-coated iron powders on which the coppercoating was applied by chemical precipitation of copper from aqueouscopper salt solutions do not respond materially to the additions of fluxand/or metal-component prior to sintering, in producing increasedstrength in the sintered body. Likewise, electrolytic copper coatings oniron powders do not respond to the flux and/or metal-componentadditions.

We have also found that strong sintered bodies composed largely of ironpowders may be made from mixtures of uncoated iron powders with thethermochemically coated iron powders, the latter being more than about50% of the total mixture and carrying sufficient copper as a coating toprovide between about 4% and 80% of copper by weight of the total ironpowder in the mixture.

In this specification, the term iron powder refers to the briquettablepowders composed almost entirely of iron and containing so little carbonthat they are readily briquettable as contrasted with the hard powders,containing larger amounts of carbon or alloying elements which areunbriquettable at pressures below about 60 tons per square inch. Thebriquetting and sintering of such hard ferrous powders coated withcopper is described and claimed in the copending application of Drapeauet al., Serial No. 52, filed June 17, 1948.

In summary, our invention broadly involves the steps of (a) providing asinterable mass composed substantially completely of iron powders, atleast a major part of the iron powders being thermochemically coatedwith copper, said iron powder mass being mixed or not, as desired, withfrom about 0.1% to 2% by weight of the coated powders of a fluxingmaterial as described herein, and/or from about to 4% by weight of thecoated powders of a white-metal-containing material as described herein;and (b sintering the so-provided sinterable mass with or without anintermediate or concurrent briquetting operation. In providing thecoated powders of the sinterable mass, the thermochemical coatingreaction is carried out by reacting the iron powder in intimateadmixture with cuprous oxide or cupric oxide or mixtures thereof, toprovide a copper coating weighing between about 4% and 30% of the weightof the iron powder. The reaction is efiected in a neutral atmosphere orin a hydrogen or other reducing atmosphere which may be carburizing ornon-carburizing with respect to the iron powder, and the reactiontemperature is between about 1000 F. and 1500" F., but is preferablybetween about 1100 F. and 1300 F. The thermochemical reaction mass isheated at the indicated temperatures for a sufiicient length of time todeposit the required weight of coating. This time may vary between about3 minutes and 60 minutes but the actual amount of time required, whetherwithin this range or more or less, may be determined readily by trial.The admixture of copper-coated iron powder with uncoated iron powder orwith the flux and/ or white-metal-containing material may be effected bymixing any combination of the latter materials with the copper-coatedpowder, or alternatively the fluxes and/or white-metal components may bemixed with the thermochemical reaction mass of iron owder and copperoxide, any uncoated iron powders desired in the mass being added afterthe thermochemical coating has been formed. In making the admixture byeither procedure, the fluxes and white-metal-containing materials whichare used should preferably be very finely divided so that the resultingadmixture will be very intimate. For example, pigment grade of zincoxide is very suitable since its fineness promotes its thoroughdispersion throughout the reaction mass. The use of about 0.1% to 1%,preferably about .2% of stearic acid or mineral oil by weight of thecopper oxide not only aids the uniform dispersion of the copper oxidebut similarly aids the dispersion of the fluxes and/or white metaloxides when these latter materials are incorporated in thethermochemical reaction mixture.

The sintering of the aforesaid provided sinterable mass is effected in ahydrogen, carbon monoxide or mixtures thereof at temperatures somewhatbelow, at or above the melting point of copper, and preferably attemperatures between about 2000 F. and 2200 F. Commercially usefulstrengths can be obtained by sintering at temperatures as low as about1800 F. The duration of the sintering operation within the indicatedrange of temperatures depends on various factors such as the selectedtemperature, the size of the body being sintered, its density (whetherbriquetted or unbriquetted), the capacity of the sintering furnace, therate of heating, etc. The optimum duration of heating can readily bedetermined by one skilled in the art.

However, a soaking period of about /g hour is generally required afterthe body has attained the desired temperature, even for small bodiesheated in about 3 to 4 minutes to temperatures of 2200 F. The inventioncontemplates the cooling of the sintered body under non-oxidizingconditions, such as by cooling in the same atmosphere as used in thesintering furnace. However, any suitably non-oxidizing cooling treatmentmay be used whether it be a gaseous reducing or inert atmosphere, an oilcooling bath or otherwise.

Many modifications may be made in the practice of the invention asdisclosed herein, and will be apparent to those skilled in the art. Wecontemplate as part of our invention all such modifications as fallwithin the scope of the following claims.

Having disclosed our invention, what we claim 1s:

1. The method of making sintered iron bodies of improved strength fromthermochemicallycoated ir-on powders, said method comprising the stepsof: providing a sinterable mass consisting essentially of an intimatemixture of (al iron powders, at least a major part of which powderscarries a copper coating amounting to between about 4% and 30% of thetotal weight of the iron powders, said coating having been applied tothe said major part of the iron powders by a thermochemical reactionbetween said. iron powder and finely-divided copper oxide attemperatures between about 1000 F. and 1500 F. in a non-oxidizingatmosphere, and (b) between about 0.1% and 2% by weight of thecoppercoated iron powder of at least one powdered fluxing materialselected from the group consisting of the alkali metal carbonates, thealkali metal nitrates, the alkali metal borates in glass form, and lime;sintering said sinterable mass in a --to=between..about4% and30*% about1000 F; and I500 F. in a non-oxidizing atmosphere, and (12') betweenabout 0.1% and 22% 'b'y'weightlof the copper-coated iron powder of atleast-one-p owd'ered fluxing; material selected from the groupconsisting of the alkali metal carbonates, the alkali metal: nitrates,the alkali metal borat'es in glass form, and lime; briquetti'ng' said'sint'erable mass; sintering' said :briquetted massin areducingatmosphere at temperatures between about 1800 F. and'2200 F;; andcooling said sin tered mass under non-oxidizing conditions.

3. The method as claimed in claim 2 wherein the fiuxi-ng material ispowdered borax glass in an'amount of about /2%.

'4. The method as claimed in claim 2 wherein a reducing atmosphere isemployed in said thermochemicalreaction.

5. A sinteredproduct asprod-uced by the methed claimed in claim 2'.

6i The-method as claimed in claim 2 wherein said sinterab-le mass alsoincludes between about and 4% of metallic tin equivalent infinelydivided form; by weight of the copper-coated iron powder.

' 7 The method as claimed in claim 2 wherein said sinterable mass alsoincludes between about 4% and 4% of metallic zinc equivalent infinelydivided form; by weight of the copper-coated ironpowder.

" vidd copper oxide at temperatures between 8-. The method as claimed inclaim 2 wherein said sinterable mass also includes between'about and 4%of metallic cadmium equivalent in finely-divided ,form', by weight ofthe coppercoated iron powder.

9. The method of making sintered iron bodies of improved strength fromthermochemieallycoated iron powders,'said method comprising-the stepsof: providing a sinterable mass consisting essentially of an intimateadmixture of (a) iron powders, at least-a major part of which powderscarries a copper coating amounting; to between about 4% and 30% ofthe'totalweight of' the iron'powders, saidcoating having beenuapplied tothe said major part of the iron powders by a, thermochemical reactionbetweensaid iron powder and finely-divided copper oxide at temperaturesbetween about 1000 F; and 1:500 F.-

in a non-oxidizing atmosphere, and (In) between about and 4% in metallictin equivalent in finely-divided form, by weight of the coppercoa'tediron powder; sintering said'sinterable mass in a reducing atmosphere attemperatures between about -1800 F. and 2200 F.; and cooling saidsintered mass in a non-oxidizing atmosphere. I

10. A sinteredproduct as produced by the method claimed. in claim 9-.

JOSEPH E. DRAPEAU, JR. JAMES H. SMITH. RICHARD J-. HALSTED.

REFERENCES CITED The following references are of record in the file ofthis patent:

UNITED vSTATES PATENTS Date

9. THE METHOD OF MAKING SINTERED IRON BODIES OF IMPROVED STRENGTH FROMTHERMOCHEMICALLYCOATED IRON POWDERS, SAID METHOD COMPRISING THE STEPSOF: PROVIDING A SINTERABLE MASS CONSISTING ESSENTIALLY OF AN INTIMATEADMIXTURTE OF (A) IRON POWDERS, AT LEAST A MAJOR PART OF WHICH POWDERSCARRIES A COPPER COATING AMOUNTING TO BETWEEN ABOUT 4% AND 30% OF THETOTAL WEIGHT OF THE IRON POWDERS, SAID COATING HAVING BEEN APPLIED TOTHE SAID MAJOR PART OF THE IRON POWDERS BY A THERMOCHEMICAL REACTIONBETWEEN SAID IRON POWDER AND FINELY-DIVIDED COPPER OXIDE AT TEMPERATURESBETWEEN ABOUT 1000* F. AND 1500* F. IN A NON-OXIDIZING ATMOSPHERE, AND(B) BETWEEN ABOUT 1/4% AND 4% IN METALLIC TIN EQUIVALENT INFINELY-DIVIDED FORM, BY WEIGHT OF THE COPPERCOATED IRON POWDER;SINTERING SAID SINTERABLE MASS IN A REDUCING ATMOSPHERE AT TEMPERATURESBETWEEN ABOUT 1800* F. AND 2200* F.; AND COOLING SAID SINTERED MASS IN ANON-OXIDIZING ATMOSPHERE.